With increasing Volatile Organic Content (VOC) restrictions, it is difficult to get a balance of pot life and dry time for coatings useful in refinish paint compositions. The main problems have been that the hydroxyl functional polyols are generally high molecular weight resins, which are viscous materials and require a lot of organic solvents in order to reduce to sprayable viscosities. It is also difficult to get the VOC low enough to be compliant with environmental restrictions. By using reactive diluents in combination with the polyol and isocyanates, lower VOC can be achieved. An excellent example of this type coating is exemplified in U.S. Pat. No. 5,214,086 and is assigned to BASF Corporation.
In the prior art, the use of diketimines, dialdimines, and hindered diamines as reactive diluents, helps to lower the viscosity and increase the solids, thus enabling coating compositions to reach required VOC limits. However, as more stringent VOC limits are being set, it has become necessary to try and achieve even lower VOCs. The use of low molecular weight hydroxyl functional polyols are difficult to use in order to reach these VOC limits. In addition, these polyols react too fast and a sufficient pot life is difficult to achieve.
An approach to a coating composition has been to mix epoxy/amine reactants with isocyanate reactants but the amine from the epoxy reaction reacts exceedingly fast with the isocyanate, leaving only an epoxy group and an hydroxyl group which do not react under ambient conditions.
We have now found that polyuroxy coating compositions overcome the prior art disadvantages and result in low VOC coatings that are especially useful as refinish paint compositions
The present invention is directed to novel coating compositions. In particular, the present invention is directed to coating compositions that comprise an epoxy resin, imine, (preferably ketimine), polyisocyanate and an active hydrogen containing compound. Coating compositions have been found to be excellent sealer compositions, are tintable, and are preferably applied wet on wet utilizing a basecoat/clearcoat or single stage topcoat over them.